Magnetic field sensors, such as Hall Effect sensors, are commonly used for sensing the relative position of one object to another. Such sensors generally provide an output dependent upon the level of magnetic flux imparted thereto. For example, sensing the relative position of one object to another may be achieved by affixing a Hall Effect sensor to one object and a magnet to the other object. As the sensor and/or the magnet are moved relative to each other, the magnetic flux imparted to the sensor varies causing associated changes in the sensor output. The sensor output may therefore be indicative of the position of the magnet.
In one configuration, the sensor may provide a binary “on” or “off” output when the magnetic flux imparted to the sensor increases or decreases beyond certain thresholds. In another configuration, the sensor may provide a linear output whereby each value of magnetic flux within a range of flux values causes a different associated sensor output, e.g. between upper and lower limits. The output of such a linear Hall Effect sensor may be indicative of the absolute position of the magnet relative to the sensor.
Magnetic field sensor position sensing configurations are effective, but involve sources of position sensing error, such as manufacturing and environmental conditions, that complicate design and limit performance. For example, the air gap, i.e. the distance between the magnet and the sensor when the magnet and sensor are in the closest relative positions, affects the flux imparted to the sensor and, thus, the sensor output. Manufacturing tolerances in the air gap may, therefore, impact position sensing. Generally, in a given configuration as the air gap is increased, the magnetic flux imparted to the sensor may significantly decrease. The maximum magnetic flux imparted to the sensor can, therefore, be significantly affected by the air gap.
Temperature variation may have a similar effect on magnetic flux imparted to a magnetic field sensor, such as a Hall Effect sensor. For example, the maximum magnetic flux imparted by a magnet may vary significantly over an anticipated application temperature range. Variation in magnetic flux can affect the performance of the position sensing system.
Additionally, as is known, Hall Effect sensors typically exhibit a range of magnetic flux values for which the sensor may, or may not, turn “on” to provide an output. For values above the range, the sensor may definitely be on, and for values below the range the sensor may definitely be off. The range of magnetic flux values for which the sensor may or may not turn “on”, i.e., above the definitely off value and below the definitely on value, is known as the “pink” zone of the Hall Effect sensor. Travel positions of a magnet which impart a magnetic flux within the “pink” zone of the Hall Effect sensor are known as the switching “gray” or “unknown” zones. When the magnet is in the “gray” zones the Hall Effect sensor may or may not turn on the Hall Effect sensor to provide an output. Variations in the magnetic flux imparted on the Hall Effect sensor by the magnet, e.g., due to air gap variation, temperature conditions, etc., may produce wide unknown zone in a position sensing system. The wide switching unknown zones may be narrowed using various mechanical techniques. These mechanical techniques, however, can also provide a source of error in position sensing.
There is therefore a need for a position sensing system and method wherein variations in magnetic flux imparted to a sensor due to manufacturing and environmental conditions is reduced or eliminated.
Although the following Detailed Description will proceed with reference being made to illustrative embodiments, many alternatives, modifications, and variations thereof will be apparent to those skilled in the art. Accordingly, it is intended that the subject matter be viewed broadly.